Journalctl used to detect errors in the boot process RHEL7 RHEL8

RHEL7 and RHEL 8 ,  Journalctl is a command used to detect errors in the boot process
To detect errors during startup, we can use journalctl :

# journalctl -b -p err

With the -p parameter we are indicating the priority of errors to display:
"Emerg" (0)
"Alert" (1)
"Crit" (2)
"Err" (3)
"Warning" (4)
"Notice" (5)
"Info" (6)
"Debug" (7)